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    sgmartin's Avatar
    sgmartin Posts: 1, Reputation: 1
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    #1

    Nov 5, 2009, 05:27 PM
    how do i prove this identity
    sin2x/sinx - cos2x/cosx = secx
    ebaines's Avatar
    ebaines Posts: 12,131, Reputation: 1307
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    #2

    Nov 5, 2009, 06:17 PM

    Remember these important identities:

    sin2x = 2sinxcosx
    cos2x = cos^2x - sin^x
    = 2 cos^x - 1
    = 1-2sin^2x.

    That second identity for cos2x looks promising, since you will be dividing by cosx. Try it, and see if you make progress.
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